<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            background-color: red;
        }
        .one{
            background-color: blue;
        }
        div button{
            background-color: yellow;
        }
        div button:hover{
            background-color: red;
            width: 100px;
            font-size: 50px;

            /* 鼠标图标 手指 */
            cursor: pointer;  
        }
        div button:active{
            background-color: yellow;
        }
    </style>
</head>
<body>
    <div>
        标签选择器
    </div>
    <div class="one">
        类选择器
    </div>
    <div>
        <button>
            后代选择器
        </button>
    </div>
    <div>
        <button>伪类</button>
    </div>
</body>
</html>